1. Field of the Invention
The present invention relates to an apparatus and method of driving a single-phase switched reluctance motor, and more particularly to a single-phase switched reluctance motor (SRM) driving apparatus and method which enables a high-speed and high-efficiency SRM by employing a plurality of sensors, and which can minimize the switching frequency of elements constituting an SRM driving section.
2. Description of the Related Art
A switched reluctance motor (SRM) is a specific type motor combined with a switching control device, wherein both its stator and rotor have a protruded pole type structure, and there exists no winding or permanent magnet of any type on the rotor part, enabling the SRM to have a very simple structure.
Since the SRM has a very simple structure, it has advantages in productivity. Also, it has a good starting characteristic and a great torque, while it requires little maintenance and repair such as a periodic exchange of brushes and so forth. Also, the structure of its driving apparatus is simplified in comparison to an induction motor driven by an inverter, and it has superior characteristics in torque per volume, efficiency, rating of the converter, etc.
Due to such superior characteristics, the SRM has been increasingly used in various fields in many countries.
FIG. 1 is a block diagram of a conventional single-phase SRM driving apparatus.
Referring to FIG. 1, the conventional single-phase SRM driving apparatus comprises a smoothing circuit section 102 for smoothing an AC current applied from a commercial AC power supply 101 to a DC voltage, a microcomputer 106, a motor driving section 103 for receiving the DC voltage supplied from the smoothing circuit section 102 and a control signal outputted from the microcomputer 106, and driving a motor 104 accordingly, and a Hall sensor 105 for detecting the position and speed of the motor 104, and outputting a detection signal to the microcomputer 106.
The operation of the conventional single-phase SRM driving apparatus as constructed above will be explained in detail with reference to FIG. 1.
The smoothing circuit section 102 smoothes the input voltage of the commercial power supply 101. The smoothed voltage is supplied to the motor driving section 103, and the motor driving section 103 supplies the voltage to the motor 104 in accordance with the control signal from the microcomputer 106.
Then, the Hall sensor 105 detects the rotating speed and phase of the motor 104 to generate a detection signal, and the microcomputer 106 controls the motor driving section 103 in accordance with the signal generated by and received from the Hall sensor 105, so that the motor driving section 103 controls the voltage supplied to the motor 104.
FIG. 2 is a view illustrating the construction of the conventional single-phase SRM and motor driving section.
Referring to FIG. 2, the conventional single-phase SRM motor 300 is a single-phase 6/6-pole SRM composed of a stator 207, a rotor 208, a magnet 209 for position detection, and a parking magnet 210.
The conventional SRM driving section 200 comprises a DC link capacitor 201 for smoothing the AC power supply and outputting a smoothed DC voltage, upper and lower switching elements 202 and 203, connected in parallel to the DC link capacitor 210, for being turned on/off in accordance with a gate driving signal from a switching driving section (not illustrated) which rotates the motor in a forward or backward direction in accordance with a rotor position signal of the SRM, a first diode 204 connected to motor windings 206 for generating a torque according to an on/off operation of the upper and lower switching elements 202 and 203, one terminal of the upper switching element 202, and one terminal of the lower switching element 203, and a second diode 205 connected between the other terminal of the upper switching element 202 and the other terminal of the lower switching element 203.
The operation of the conventional single-phase SRM as constructed above will be explained in detail.
First, if the AC power supply is applied, the DC link capacitor 201 smoothes it to a DC voltage. This smoothed DC voltage is supplied to the motor windings 206 in accordance with the switching operation of the upper and lower switching elements 202 and 203.
Specifically, the upper and lower switching elements 202 and 203 are turned on according to the position of the rotor 208 and the stator 207 of the SRM, and this causes a current path is formed through the DC link capacitor 201, upper switching element 202, motor windings 206, and lower switching element 203. Accordingly, a voltage is excited in the motor windings 206, a magnetic force is generated from the stator 207, and thus the SRM rotates by the magnetic force acting on the rotor 208.
If the upper and lower switching elements 202 and 203 are simultaneously turned off as the SRM rotates, a phase current being applied to the motor windings 206 is eliminated through the first diode 204, motor windings 206, second diode 205, and DC link capacitor 201.
As described above, the conventional SRM is driven by supplying or intercepting the voltage to the motor in accordance with the on/off operation of the upper and lower switching elements 203 and 204 which constitute the motor driving section.
Here, the control signal applied to the upper and lower switching elements 202 and 203 is generated by detecting the rotating speed and the phase of the motor through the Hall sensor as shown in FIG. 1, and the microcomputer pulse-width-modulates the output signal of the Hall sensor and controls the on/off operation of the upper and lower switching elements 202 and 203 in accordance with a duty ratio of pulse width modulation (PWM).
FIG. 3 is a graph illustrating an inductance profile according to the phase change of the conventional single-phase SRM.
Hereinafter, the voltage supplying operation of the motor driving section to the motor will be explained in detail with reference to FIGS. 2 and 3.
According to the SRM having the structure as shown in FIG. 2, when a protruded pole part 207-1 of the stator 207 and a protruded pole part 208-1 of the rotor 208 are in an alignment state, the inductance of the SRM becomes greatest, while when they are in a misalignment state, the inductance becomes smallest.
Also, in the case of the conventional SRM having the 6/6-pole structure, the maximum point and the minimum point of inductance alternately appear every phase of 30xc2x0.
In order to drive the SRM, the Hall sensor (not illustrated) detects the position of the rotor 207, generates and outputs the control signal to the microcomputer when a position a of the rotor 207 moves to a position b or bxe2x80x2 of the stator 208, i.e., at the time point when the inductance increases. Then, the microcomputer generates the control signal, and supplies the current to the motor windings 206 by controlling the motor driving section to supply the voltage.
FIGS. 4a and 4b are views illustrating a normal parking position and an abnormal position of the single-phase SRM.
When the SRM is stopped, it is parked by mutual attraction acting between an N pole of a parking magnet 401a and an S pole of a magnet 404a fixed to a rotor 402a, and between an S pole of the parking magnet 401a and an N pole of the magnet 404a, respectively, as shown in FIG. 4a, and thus a normal parking state of the SRM is maintained for the next rotation.
However, as occasion requires, when a rotor 402b is stopped, the SRM may be parked by mutual repulsion acting between an N pole of a magnet 404b fixed to the rotor 402b and an N pole of a parking magnet 401b, and between an S pole of the magnet 404b and an S pole of the parking magnet 401b, respectively, and this causes the SRM to be in an abnormal parking state.
As described above, the conventional single-phase SRM has the following problems:
First, in spite of the increase of voltage applied to the motor, the increasing speed of current is slower than that of the voltage, and thus it is difficult to use the conventional SRM for a product that requires a high-speed rotation.
Second, in the conventional high-speed SRM, the switching loss occurs in the upper and lower switching elements due to frequent switching operations since the switching elements are controlled by the adjustment of the PWM duty ratio from a low speed to a high speed, and this causes electromagnetic waves to be greatly generated.
Third, in the case that the rotor of the motor is in the abnormal parking position, the rotor may not rotate further or may operate unstably even if any current flows to the stator for the further rotation of the motor.
Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and a first object of the present invention is to provide a single-phase switched reluctance motor (SRM) driving apparatus and method which enables a high-speed and high-efficiency SRM by driving the SRM with a start sensor and an operation sensor separately provided.
It is a second object of the present invention to provide a single-phase SRM driving method which can minimize the switching frequency of elements for driving the SRM.
It is a third object of the present invention to provide a single-phase SRM driving method which can stably drive the SRM by preventing an abnormal parking of the SRM.
In order to achieve the above objects, according to the present invention, there is provided a single-phase SRM driving apparatus comprising a smoothing circuit section for smoothing an input power supply, a motor driving section for receiving a voltage smoothed by the smoothing circuit section and supplying the voltage to a motor in accordance with a control signal, a plurality of sensors for sensing a rotating speed and a phase of the motor, and a microcomputer for receiving one selected among signals sensed by the plurality of sensors, and outputting the control signal for controlling the motor driving section.
In another aspect of the present invention, there is provided a single-phase SRM driving method comprising the steps of (a) sensing a rotating speed and a phase of a motor through a plurality of sensors and producing sensed signals, (b) selecting one among the plurality of sensors, receiving the sensed signal produced from the selected sensor, and producing a control signal for controlling a voltage supplied to the motor, (c) detecting the rotating speed of the motor, and comparing the sensed rotating speed with a reference speed determined by a system, and (d) selecting another sensor if the sensed rotating speed of the motor is faster than the reference speed as a result of comparison at step (c), and producing a control signal for controlling the voltage supplied to the motor in accordance with the sensed signal produced from the selected sensor.
In still another aspect of the present invention, there is provided a single-phase SRM driving method comprising the steps of (a) initially aligning a rotor and a stator of a motor when a power supply is inputted, (b) waiting for a predetermined time after the rotor and the stator of the motor are aligned at step (a), (c) applying a secession pulse for an initial start of the motor after the predetermined time elapses, (d) receiving a signal produced from a first sensor, and increasing a rotating speed of the motor started at step (c) by adjusting a duty ratio of pulse width modulation (PWM) of the signal, (e) comparing the rotating speed of the motor with a reference speed determined by a system, and (f) if the rotating speed of the motor is faster than the reference speed as a result of comparison, receiving a signal produced from a second sensor, and controlling the rotating speed of the motor in a dwell time.